access addressing or other information in the entry besides the actual data being routed, look at the frame in the

fields

slot. However, use of the

fields

slot is

for special cases only and is generally discouraged. This is because it works only in the In/Out Box, and so ties your stationery to it. If you need to use the

fields

slot

in your stationery, you should always check for the existence of this slot before using it, and you must be able to handle the case where it is missing.

Also, view definitions to be used by the In/Out Box can have a

rollScrolling

slot. This slot contains a Boolean value. If you set this slot to

true

, the view is

treated as a paper roll-based view that specifies its height. In this case, the In/Out Box handles scrolling within the view for you, when the user taps the built-in scroll arrows. If the

rollScrolling

slot is set to

nil

, scrolling functionality must be

provided by the view definition itself, typically with scroll arrows inside the view.

If the

rollScrolling

slot is set to

true

, the target item must have a

height

slot that specifies the height of the item in pixels.

Note that the

newtEditView

proto sets the

rollScrolling

slot to

true

, and

is useful for creating a paper roll-based view definition.

Advanced Alias Handling

21

For sending data, an application may register a routing format that stores a sent object as an alias in the In Box. In fact, you can set a slot,

storeAlias

, in

the routing format that allows this to happen. When such an object is to be sent by the transport, the Routing interface automatically resolves the alias into the actual object that is sent.

However, in some circumstances, you might want to provide your own custom alias handling. For example, you might want to store an object in the In Box as a complex frame consisting of some directly stored data and some slots that contain aliases. In this case, you would override the routing format method

MakeBodyAlias

to construct your own object.

When the system needs to access the item, such as when it is viewed in the In/Out Box, it sends the message

ResolveBody

to the format. You must override this

method and use it to resolve the alias you constructed in the

MakeBodyAlias

method.

Note that if the send operation fails, the Out Box continues to store the original unresolved entry.